A resin rotator in which a resin is retained in a fiber substrate has high durability, and is suitably used as the material of a resin gear or the like for use in vehicle components, industrial components, and so forth.
JP 2001-295913 A describes a fiber substrate for fabrication of a resin gear. The fiber substrate is formed by weaving or knitting a thread into a tubular member and rolling the tubular member inside out from an end portion into a doughnut shape. JP 2001-295913 A also describes a resin gear formed by forming teeth on the fiber substrate which is impregnated with a resin so that the resin is retained in the fiber substrate.
JP 2001-295913 A further describes a construction in which two fiber substrates are superposed in a mold with a metal bushing interposed between the two fiber substrates in order to improve the bonding strength between the fiber substrates and a retainer provided in the metal bushing.
JP 11-227061 A describes a doughnut-shaped fiber substrate that is different from the doughnut-shaped fiber substrate discussed above, and describes a method of manufacturing a resin gear, in which a formed sheet formed from a thermosetting resin and short fibers by a filtering-dehydration system, is pressed into formed sheet pieces, and a plurality of the formed sheet pieces are stacked and are heated and pressurized in a mold.
In the resin gears described in JP 2001-295913 A and JP 11-227061 A, the fibers are hardly tangled at the superposition interface between the two fiber substrates or the stacking interface between the formed sheet pieces, and separation may be easily caused at the interface depending on the usage.
In addition, the bonding strength between the fiber substrates and the metal bushing may be insufficient. Therefore, the durability of the resin gears may be insufficient depending on the usage.
In order to address such issues, it is proposed to produce an aggregate of short fibers by a filtering-dehydration method using a mold.
JP 2001-001413 A discloses a method of manufacturing an aggregate of short fibers and a thermosetting resin in which slurry containing a mixture of short fibers and a thermosetting resin is pressure- or vacuum-dehydrated in a water-permeable mold.
However, a thermosetting resin that can be dispersed in water has low flowability and does not provide sufficient wettability at the interface between the thermosetting resin and the fibers, and therefore does not provide durability suitable for practical use.
JP 2005-096173 A discloses a method of fabricating a fiber-reinforced resin complex. In the method, charging of short fibers and pouring of a resin are performed in the same mold having a fluid outlet port and the short fibers and the resin are heated and pressurized in the mold.
In the method, however, it is difficult to dispose a metal bushing in a center portion of a resin rotator. In addition, the poured resin may leak through the entire mold which is formed from a wire net or the like, thereby making it difficult to take out a formed object after the resin has been cured. Moreover, the mold may be clogged, and may not be used over and over (continuous production).
JP 2007-138146 A discloses a method of manufacturing a resin gear. In this method, a seamlessly formed cylindrical fiber substrate, which is obtained by a filtering-dehydration method, is heated and pressurized as an aggregate of short fibers in a mold.
However, JP 2007-138146 A does not disclose at all a method that improves the bonding strength between the fiber substrate and a metal bushing.
In order to address the issues of JP 2001-001413 A, JP 2005-096173 A, and JP 2007-138146 A discussed above, JP 2011-152729 A describes a method of fabricating a fiber substrate by using the same mold and apparatus, in which short fibers are accumulated around the outer peripheral portion of a metal bushing by a filtering-dehydration method to fabricate a fiber aggregate that surrounds the outer peripheral portion of the bushing, and thereafter the fiber aggregate is compressed by driving a pressing machine in the vertical direction which corresponds to the axial direction of a rotary shaft.
In the fabrication, a thermosetting resin is not used in the filtering-dehydration method to fabricate the fiber aggregate, but the fiber aggregate is impregnated with the thermosetting resin after the formation of the fiber aggregate. Thus, sufficient wettability is provided at the interface between the resin and the fibers. The metal bushing can be easily disposed in a center portion of a resin rotator, which eliminates the risk of a resin leak. In addition, the bonding strength between the fiber substrate and the metal bushing can be improved.
In the fabrication described in JP 2011-152729 A, however, slurry is poured onto a member called “upper support member”, and short fibers may remain on the “upper support member”. In such a case, the amount of short fibers per product may be fluctuated. Further, the short fibers may be caught in a gap between molds when compressing the fiber aggregate, which may break the molds to interrupt continuous production.
It is an object of the present invention to provide a method of manufacturing a fiber substrate that suffers little fluctuation in amount of short fibers among individual products and causes no damage to the molds to enable continuous production.
It is also an object to provide a method of manufacturing a resin rotator and a resin rotator manufactured by the method in which a fiber substrate is impregnated with a resin and the resin is cured.